This invention relates to a screw fixing plug used to mount instruments or the like to a construction article of concrete or mortar using a combination of the plug and a screw.
Heretofore, in mounting an instrument or the like to a construction article of concrete or mortar using screws, after forming a starting hole by drilling in the concrete or mortar, a cylindrical plug is inserted into the starting hole, a screw is inserted through an instrument superposed on the concrete or mortar, and the screw is tightened into the plug in the starting hole. The screw thus expands the plug, so that the instrument can be tightened to the concrete or mortar.
The conventional plug aims to obtain tightening force by pressing the plug against the inner wall of the starting hole by uniformly expanding the plug by the screw, thus preventing development of a gap between the screw and the starting hole. But since the plug is structured so as to prevent slip between the plug and concrete or mortar by the friction between the outer surface of the expanded plug and the inner wall of the hole in the concrete or mortar, slipping of the plug tends to occur relative to concrete or mortar, because the concrete or mortar is a material that is brittle and easily broken.
An object of this invention is to provide a screw fixing plug which can ensure biting of threads into concrete or mortar, when the plug is unevenly deformed and moved. The threads bite directly into both the concrete or mortar and the plug when the screw is tightened into the plug that is inserted into the starting hole. This increases the tightening force of the plug, and provides a combination of such a plug and a screw.